Image Number 18 for United States Patent #3950103.
A method and apparatus for numerical determination of the distribution of magnitude and phase of a time harmonic electromagnetic, particularly an optical, wave field by using the wavefront of a reference wave as the optical reference surface and by introducing additional information to the recording process such that the field becomes uniquely determined and this is realized by the recording of three interference fringe patterns which belong to variations of the reference field distribution. A reference field is chosen whose spatial distribution is similar to the unknown field whereby fringes are obtained the position of which varies slowly with the recording coordinates. The recorded data are numerically evaluated and this may be done conveniently in a computer. After these measurements are made the reference beam is shifted by an optical element e.g. a prism, gaseous wedge, electro-optical diffraction device placed in the reference optical path and a second set of measurements is made. In this way a reference field whose spatial distribution is not known precisely is introduced but the system is such that the reference spatial distribution information is used and then eliminated from the information finally obtained on the unknown wavefield.